In crank-type Stirling engines, a piston and a displacer are linked to a rotating shaft by means of a linking mechanism so that the shaft is driven in rotation by the reciprocation of the piston and the displacer is driven in reciprocation by the rotation of the crank shaft. In such an engine both the piston and the displacer have periodic, reciprocating motions which are approximately sinusoidal. They have the same period and a selected phase angle between their respective periodic motions. The operating characteristics of the engine are in part dependent upon the stroke of each as well as the magnitude of the phase angle between their periodic motions.
A variety of linking means for drivingly connecting reciprocating bodies to rotating bodies are shown in the prior art. Those which have been applied in Stirling engines include not only the conventional crank and connecting rod but also rhombic drives, bell cranks, cams and wobble plates.
Slotted yoke drives have long been known in the art and include both the simple slotted yoke in which a pin or roller operates in a slot and the scotch yoke in which wear is reduced through the use of a slide operating in the slot to which the crank pin is rotatably mounted. However, these prior art slotted yokes have the slot essentially perpendicular to the axis of motion of the yoke.
A few patents such as U.S. Pat. No. 3,152,272, show a single yoke with a slot which is inclined to the axis of the reciprocating motion. This is done, however, for reducing friction and has nothing to do with accomplishing a phase relationship between two reciprocating bodies.
One patent, U.S. Pat. No. 963,449, shows a pair of yokes with slots which are essentially perpendicular to the axis of motion of the yokes but which have an intermediate transition area in which a small portion of the slots are inclined to the axis of reciprocating motion. This would not be suitable for Stirling engine applications because of the simultaneous and lengthy dwell and the abrupt changes in the slots.